Compounds containing a perfluoropolyether moiety generally have very small surface free energy to have water and oil repellency, chemical resistance, lubricity, releasing property, and antifouling property. Making use of these properties, they are widely used as, for example, treatment agents to make paper or fiber water- and oil-repellent, and foul-resistant, lubricants for magnetic storage media, oil repellent agents for precision apparatuses, releasing agents, cosmetics, and protective films.
As a coating agent used for glass, pottery, and plastic films, a silane coupling agent is well known. The silane coupling agent has an organic group and a reactive silyl group, generally alkoxysilyl group, per molecule. The alkoxysilyl group is hydrolyzed by atmospheric moisture to form a coating layer by autocondensation reaction. It also chemically or physically binds to a surface of a substrate such as glass to fix the coating. Making use of this property, the silane coupling agent is widely used as a coating agent.
Japanese Patent Application Laid-Open No. 10-59745 discloses a fluoroalkyl silane compound. A coating made from the compound is water repellent and durable. However, once a waterdrop sticks on the coating, the waterdrop does not easily slide down. Waterdrop sliding property of a coating can be evaluated by sliding-down angle of waterdrop, hereinafter referred to waterdrop sliding-down angle. The angle is measured by placing a drop of 10 μl water on a coated surface of a substrate which is then tilted gradually and an angle at which the waterdrop starts sliding is measured.
Japanese Patent Application Laid-Open No. 2002-12452 discloses a coating of window glass of vehicles which coating is made of a copolymer of fluoroalkyltrichlorosilane with dimethylsiloxane having terminal silanol groups. The coating has good waterdrop sliding property. However, water repellency is not so durable: A water contact angle of a fresh coating is about 100 degrees but it is decreased to below 100 degrees by abrasion or scrubbing.
Japanese Patent Application Laid-Open No. 2003-238577 discloses a silane compound having a perfluoropolyether moiety introduced to a molecule to impart oil-repellency. Glass coated with the compound is water- and oil-repellent and easy to clean off oily dirt. However, its waterdrop sliding-down angle is larger than 10 degrees, which is not desirable.
Window glass of automobiles, trains, ships, airplanes, or high-rise buildings preferably has a waterdrop sliding-down angle small enough for the waterdrop to easily slide down or to be blown away by wind, because such glass allows reduced time and costs of maintenance. The glass preferably is oil-repellent, too, to clean off oily dirt and excretory substances of insects or animals easily. Surface of sanitary ware, kitchen ware and sewage pipes are preferably oil- and water-repellent.